At the basis of the marine Arctic food web, there are several carbon sources including ice-associated (sympagic) algae that live primarily in sea ice, melt ponds or underneath sea ice; pelagic algae that live primarily in open waters; terrestrial detritus that got incorporated into sea ice forming on the Siberian Shelf and being transported with the transpolar drift across the Central Arctic Ocean (CAO); and detritus that derives with currents from the Atlantic ocean. Copepods and amphipods are diverse and often biomass-dominant zooplankton groups in the CAO that include taxa specialised in feeding on algae and small heterotrophs, on sinking detritus or other zooplankton. Gelatinous (cnidaria, appendicularia) and semi-gelatinous (chaetognaths) taxa, ostracods, pteropods, euphausiids and pelagic decapods are other important zooplankton groups in the CAO that likewise feed on a range of food sources. With the loss of Arctic sea ice, the relative importance of ice-associated carbon in the Arctic food web became a central research topic, and multiple trophic marker approaches have been developed to distinguish between pelagic and sympagic carbon transfer to higher trophic levels. During the MOSAiC expedition in the CAO (2019-2020), zooplankton was sampled weekly to fortnightly. A range of nets were used to sample either horizontally underneath the sea ice or vertically from a maximum depth of 2000 m to the surface. Onboard, abundant zooplankton taxa were sorted from each catch, photographed, rinsed with freshwater to remove salt and frozen at -80 degrees Celsius for subsequent analysis of their total dry mass (DM), lipid content, lipid classes and a suite of trophic markers, including bulk stable isotopes (BSI), phytosterols (PS), total fatty acids (TFA), total fatty alcohols (TFAlc), highly-branched isoprenoids (HBI) and the carbon isotopic composition of key FA and FAlc (CSIA-FA; CSIA-FAlc). We had ~10 target species that were sampled in all seasons (the copepods C. hyperboreus, C. glacialis, Metridia longa, the ice amphipods Apherusa glacialis and Eusirus spp., the pelagic amphipods Themisto abyssorum and T. libellula, the euphausiid Thysanoessa spp., chaetognaths and the shrimp H. glacialis). Further zooplankton taxa were collected when available in the net catches and time permitted. Additionally, Polar cod was collected in early and late summer. The initial separation of the various trophic markers was carried out at the University of Plymouth. After estimating the total DM, subsamples for BSI were sent to the Littoral, Environment and Societies Joint Research Unit stable isotope facility (CNRS - University of La Rochelle, France) for analysis. Three internal standards were added to the samples used for lipid analysis to quantify the TFA, TFAlc, PS and HBI content. As a first step, the total lipid content of the animals was extracted in dichloromethane : methanol. The lipid samples were split into two equal subsamples, one was sent to the Alfred-Wegener-Institute (AWI) in Bremerhaven/Germany for FA and FAlc analyses and the second was used for PS and HBI analyses in Plymouth. This dataset is linked to a manuscript that assesses trophic relationships in the CAO to understand the carbon fluxes in the current Arctic food web and to predict potential changes in a future ice-free Arctic. Contributions by KS were funded by the UK's Natural Environment Research Council MOSAiC Thematic project SYM-PEL: "Quantifying the contribution of sympagic versus pelagic diatoms to Arctic food webs and biogeochemical fluxes: application of source-specific highly branched isoprenoid biomarkers"/ (NE/S002502/1). CJA, RGC, CEG, KMS and RJ were funded by the US National Science Foundation Office of Polar Programs (OPP-1824447 and OPP-1824414).

We present the Weddell Sea Benthic Dataset (WSBD), a computer vision-ready collection of high-resolution seafloor imagery and corresponding annotations designed to support automated analysis of Antarctic benthic communities. The dataset comprises 100 top-down images captured during RV Polarstern Expedition PS118 (cruises 69-1 and 69-6) in 2019, using the Ocean Floor Observation and Bathymetry System (OFOBS) in the Weddell Sea, Antarctica. A subset of this imagery was manually annotated by ecologists at the British Antarctic Survey (BAS) to support ecological analyses, including benthic community composition and species interaction studies. These annotations were subsequently standardised into 25 morphotypes to serve as class labels for object detection tasks. Bounding box annotations are provided in COCO format, alongside the training, validation, and test splits used during model development at BAS. This dataset provides a benchmark for developing and evaluating machine learning models aimed at enhancing biodiversity monitoring in Antarctic benthic environments. This work was funded by the UKRI Future Leaders Fellowship MR/W01002X/1 'The past, present and future of unique cold-water benthic (sea floor) ecosystems in the Southern Ocean' awarded to Rowan Whittle.

This dataset presents concentration of microplastics in snow from remote Antarctic camps: Union Glacier, Schanz Glacier and the South Pole. Refined automated FTIR techniques enabled interrogation of microplastics (including fibres) to a lower detection limit of 11 micrometers in Antarctic snow for the first time. Microplastics were pervasive (73 - 3099 MP L/1). The majority (95 percent) measured less than 50 micrometers, indicating that previous microplastic reports in Antarctica may be underestimated, due to analytical restrictions. Plastic polymer composition and concentration did not vary significantly between sites, with dominant polymers being polyamide (PA), polyethylene terephthalate (PET), polyethylene (PE) and synthetic rubber. Results indicate that even in the earth's most remote regions, humans are leaving a plastic legacy in the snow, illustrating the importance of remote, cryospheric regions as critical study sites for determining temporal fluxes in microplastic pollution. Funding: All fieldwork was supported and financed by Airbnb.